By use of a technique for transplantation of kidneys into the neck of sheep and of measurement of renin activity by radioimmunoassay, certain interrelationships of renal-adrenergic receptors and sodium control will be examined in the context of renin secretion. The cervical transplant preparation appears to permit basic studies of renal function and renin secretion in conscious sheep during steady-state conditions. Specific studies initiated will attempt to establish a hierarchy of importance in terms of the various control mechanisms of renin secretion.